A conventional laundry treating apparatus includes a cabinet forming an external appearance, a tub provided inside the cabinet, a drum rotatably provided inside the tub to wash laundry, and a motor of which rotary shaft is fixed to the drum by passing through the tub to rotate the drum.
The drum may be rotated without maintaining dynamic equilibrium depending on a position of laundry stored therein.
Dynamic equilibrium means ‘the state that a centrifugal force or a moment made by the centrifugal force is 0 with respect to a rotary shaft when a rotor is rotated’. In case of a rigid body, if mass distribution of the rigid body is uniformly maintained around the rotary shaft, dynamic equilibrium is maintained.
Therefore, dynamic equilibrium in the laundry treating apparatus may be understood that mass distribution of laundry is within an allowable range around the rotary shaft of the drum when the drum is rotated in a state that laundry is stored in the drum (the case that the drum is rotated while being vibrated within the allowable range).
In contrast, the state that dynamic equilibrium has been broken (i.e., unbalance) in the laundry treating apparatus means that mass distribution is not maintained uniformly around the rotary shaft of the drum when the drum is rotated. This unbalance is generated when laundry is not distributed uniformly inside the drum.
If the drum of the unbalance state is rotated, the drum is vibrated, and the vibration of the drum is delivered to the tub or the cabinet, whereby a problem occurs in that noise is caused.
The conventional laundry treating apparatus includes balancing units to solve unbalance of the drum. The balancing units provided in the conventional laundry treating apparatus are ball balancers or fluid balancers having a ball or a fluid received in a housing fixed to the drum.
The ball balancer or the fluid balancer included in the conventional laundry treating apparatus functions to control unbalance by moving the ball or the fluid to an opposite side of a direction where laundry causing unbalance is located when a rotation track of the drum wobbles by means of the laundry causing unbalance.
However, the aforementioned unbalance control is useful for a steady state that vibration of the drum is within a certain range, whereas a problem occurs in that the unbalance control is not effective at a transient vibration state of the drum. Also, the conventional balancing unit has a structure that it is difficult to immediately solve unbalance (actively solve unbalance) when unbalance is generated.